Heat pump device, heat pump system, and method for controlling inverter

ABSTRACT

An object of the present invention is to maintain a heating amount constant when a compressor is heated at the time of shutdown of the compressor, regardless of the influences of production tolerance and environment variations. An inverter control unit causes an inverter to generate a high-frequency AC voltage having a de-energized section in which a voltage applied from the inverter to a motor is zero between a section in which the voltage is positive and a section in which the voltage is negative. At this time, the inverter control unit detects a value of a current flowing to the inverter in a detection section residing from immediately before a start of the de-energized section to immediately after an end of the de-energized section, and causes the inverter to generate a high-frequency AC voltage adjusted according to the detected current value.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of International Patent Application No. PCT/JP2011/060396 filed on Apr. 28, 2011.

The present invention relates to a heating method of a compressor used in a heat pump device.

BACKGROUND

In Patent Literature 1, there is a description of supplying a high-frequency low voltage to a compressor during shutdown at the time of heating. In Patent Literature 2, there is a description of supplying a single-phase AC voltage of 25 kHz, which is a higher frequency than that at the time of a normal operation, to a compressor, when the environment of an air conditioner has a low temperature.

The techniques described in Patent Literatures 1 and 2 are for heating the compressor or keeping the compressor warm to facilitate a lubricating effect inside the compressor by applying a high-frequency AC voltage to the compressor in accordance with drop of the ambient temperature.

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Utility Model Laid-open No. 60-68341

Patent Literature 2: Japanese Patent Application Laid-open No. 61-91445

TECHNICAL PROBLEM

When the high-frequency AC voltage is supplied to the compressor, it becomes difficult to accurately measure a value of a current flowing to the compressor, and it is difficult to appropriately control a heating amount without influences of production tolerance and environment variations. In Patent Literatures 1 and 2, there is no description of how to appropriately control the heating amount, when the high-frequency AC voltage is supplied to the compressor.

SUMMARY

An object of the present invention is to maintain the heating amount of the compressor constant, regardless of the influences of production tolerance and environment variations, when the high-frequency AC voltage is supplied to the compressor to heat the compressor.

The present invention provides a heat pump device comprising:

a compressor having a compression mechanism for compressing a refrigerant;

a motor that actuates the compression mechanism provided in the compressor;

an inverter that applies a predetermined voltage to the motor; and

an inverter control unit that causes the inverter to generate a high-frequency AC voltage having a de-energized section in which the voltage applied from the inverter to the motor is zero between a section in which the voltage is positive and a section in which the voltage is negative,

wherein the inverter control unit includes:

a current-value detection unit that detects a value of a current flowing to the inverter in a detection section from immediately before a start of the de-energized section to immediately after an end of the de-energized section;

and a high-frequency-voltage generation unit that causes the inverter to generate a high-frequency AC voltage according to a current value detected by the current-value detection unit.

In the heat pump device according to the present invention, a current value is detected during a period from immediately before the start of the de-energized section to immediately after the end of the de-energized section.

Accordingly, a peak value of a current when the high-frequency AC voltage is applied can be detected. By controlling the high-frequency AC voltage according to the peak value, the current caused to flow to the motor can be set to a desired value. As a result, a heating amount of the compressor can be maintained constant, regardless of the influences of production tolerance and environment variations.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a configuration of a heat pump device 100 according to a first embodiment.

FIG. 2 is a diagram showing a configuration of an inverter 9 according to the first embodiment.

FIG. 3 is a diagram showing a configuration of an inverter control unit 10 according to the first embodiment.

FIG. 4 is a diagram showing input/output waveforms of a PWM-signal generation unit 26 in the first embodiment.

FIG. 5 is a chart showing eight switching patterns in the first embodiment.

FIG. 6 is a diagram showing a configuration of a heating determination unit 12 in the first embodiment.

FIG. 7 is a flowchart showing an operation of the inverter control unit 10 according to the first embodiment.

FIG. 8 is a diagram showing a configuration of the inverter control unit 10 according to a second embodiment.

FIG. 9 is a timing chart when a phase ηp and a phase θn are alternately switched by a selection unit 23 at a timing of a top and a bottom of a carrier signal.

FIG. 10 is an explanatory diagram of changes of a voltage vector shown in FIG. 9.

FIG. 11 is a timing chart when the phase ηp and the phase ηn are alternately switched by the selection unit 23 at a timing of a bottom of a carrier signal.

FIG. 12 is an explanatory diagram of a rotor position of an IPM motor.

FIG. 13 is a graph showing change of a current depending on a rotor position.

FIG. 14 is a diagram showing an applied voltage when ηf is changed with a lapse of time.

FIG. 15 is a diagram showing currents flowing to respective U-, V- and W-phases of a motor 8 when ηf is 0 degree (0 degree in a U-phase (V4) direction), 30 degrees, and 60 degrees.

FIG. 16 is a diagram showing a configuration of the inverter control unit 10 according to a third embodiment.

FIG. 17 is a chart in which a voltage and a current of the motor 8 are indicated on the timing chart shown in FIG. 9.

FIG. 18 is a diagram showing a configuration of the heating determination unit 12 according to the third embodiment.

FIG. 19 is a graph showing a relation between power required for causing a liquid refrigerant stayed in the compressor 1 to leak outside and a current value required for acquiring the power.

FIG. 20 is an explanatory chart of a process when a DC offset is superposed on a motor current.

FIG. 21 is a diagram showing a configuration of the inverter 9 in a fourth embodiment.

FIG. 22 is a chart in which a voltage and a current of the motor 8 and a current detected by a DC-current detection unit 42 are indicated on the timing chart shown in FIG. 9.

FIG. 23 is a diagram showing a configuration of the inverter 9 in a fifth embodiment.

FIG. 24 is a chart in which a voltage and a current of the motor 8 and a current detected by an inverter-current detection unit 43 are indicated on the timing chart shown in FIG. 9.

FIG. 25 is a circuit configuration diagram of the heat pump device 100 according to a sixth embodiment.

FIG. 26 is a Mollier chart of a state of a refrigerant of the heat pump device 100 shown in FIG. 25.

DESCRIPTION OF EMBODIMENTS First Embodiment

In a first embodiment, a basic configuration and operations of a heat pump device 100 are explained.

FIG. 1 is a diagram showing a configuration of the heat pump device 100 according to the first embodiment. The heat pump device 100 according to the first embodiment includes a refrigeration cycle in which a compressor 1, a four-way valve 2, a heat exchanger 3, an expansion mechanism 4, and a heat exchanger 5 are sequentially connected via a refrigerant pipe 6. A compression mechanism 7 that compresses a refrigerant and a motor 8 that actuates the compression mechanism 7 are provided in the compressor 1. The motor 8 is a three-phase motor including windings of three phases (U-phase, V-phase, and W-phase).

An inverter 9 that applies a voltage to the motor 8 to drive it is electrically connected to the motor 8. The inverter 9 applies voltages Vu, Vv and Vw to the U-phase, the V-phase and the W-phase windings of the motor 8, respectively.

The inverter 9 is electrically connected with an inverter control unit 10 including a high-frequency-voltage generation unit 11 and a heating determination unit 12 (state detection unit). The inverter control unit 10 determines whether the motor 8 needs to be heated based on a bus voltage Vdc that is a power supply voltage of the inverter 9, transmitted from the inverter 9, and a value of a current I flowing to the motor 8. When the motor 8 needs to be heated, the inverter control unit 10 outputs a PWM (Pulse Width Modulation) signal (drive signal) to the inverter 9.

FIG. 2 is a diagram showing a configuration of the inverter 9 according to the first embodiment. The inverter 9 includes an AC power supply 13, a rectifier 14 that rectifies a voltage supplied from the AC power supply 13, a smoothing capacitor 15 that smoothes the voltage rectified by the rectifier 14 to generate a DC voltage (bus voltage Vdc), and a bus-voltage detection unit 16 that detects the bus voltage Vdc generated by the smoothing capacitor 15 and outputs the bus voltage to the inverter control unit 10.

The inverter 9 has a voltage application unit 19 using the bus voltage Vdc as a power supply. The voltage application unit 19 is a circuit in which three series connection portions of two switching elements (17 a and 17 d, 17 b and 17 e, and 17 c and 17 f) are connected in parallel, and reflux diodes 18 a to 18 f that are connected in parallel to the respective switching elements 17 a to 17 f are provided. The voltage application unit 19 drives the respective switching elements in accordance with PWM signals UP, VP, WP, UN, VN and WN, respectively, transmitted from the inverter control unit 10 (17 a driven by UP, 17 b driven by VP, 17 c driven by WP, 17 d driven by UN, 17 e driven by VN, and 17 f driven by WN). The voltage application unit 19 applies the voltages Vu, Vv and Vw according to the driven switching elements 17 to the U-phase, V-phase and W-phase windings of the motor 8, respectively.

Furthermore, the inverter 9 includes a current detection unit 20 that detects the current I flowing from the inverter 9 to the motor 8 by applying the voltages Vu, Vv and Vw to the U-phase, V-phase and W-phase windings of the motor 8, respectively, to output the current I to the inverter control unit 10.

FIG. 3 is a diagram showing a configuration of the inverter control unit 10 according to the first embodiment.

As described above, the inverter control unit 10 includes the high-frequency-voltage generation unit 11 and the heating determination unit 12. The heating determination unit 12 is explained later, and the high-frequency-voltage generation unit 11 is explained here.

The high-frequency-voltage generation unit 11 includes table data 21, an external input unit 22, a selection unit 23, an integrator 24, a voltage-command generation unit 25, and a PWM-signal generation unit 26.

The selection unit 23 selects and outputs any one of a voltage command value Vc outputted from the heating determination unit 12, a voltage command value Vt recorded in the table data 21, and a voltage command value Va inputted from the external input unit 22 as a voltage command value V*. The selection unit 23 also selects and outputs either a rotation-speed command value wt recorded in the table data 21 or a rotation-speed command value ωa inputted from the external input unit 22 as a rotation-speed command value ω*.

The integrator 24 obtains a voltage phase θ based on the rotation-speed command value ω* outputted by the selection unit 23.

The voltage-command generation unit 25 generates and outputs voltage command values Vu*, Vv* and Vw* using the voltage command value V* outputted by the selection unit 23 and the voltage phase θ obtained by the integrator 24 as inputs thereto.

The PWM-signal generation unit 26 generates the PWM signals (UP, VP, WP, UN, VN and WN) based on the voltage command values Vu*, Vv* and Vw* outputted by the voltage-command generation unit 25 and the bus voltage Vdc, and outputs the PWM signals to the inverter 9.

Now, description is made for a generation method of generating the voltage command values Vu*, Vv* and Vw* in the voltage-command generation unit 25 and a method of generating the PWM signal in the PWM-signal generation unit 26.

FIG. 4 is a chart showing input/output waveforms of the PWM-signal generation unit 26 according to the first embodiment.

For example, the voltage command values Vu*, Vv* and Vw* are defined as cosine waves (sine waves) having phases different by 2π/3 as shown in Equations (1) to (3). Herein, V* denotes an amplitude of the voltage command value, and θ denotes a phase of the voltage command value.

Vu*=V*cosθ  (1)

Vv*=V*cos(θ−(⅔)π)  (2)

Vw*=V*cos(θ+(⅔)π)  (3)

The voltage-command generation unit 25 calculates the voltage command values Vu*, Vv* and Vw* according to Equations (1) to (3) based on the voltage command value V* outputted by the selection unit 23 and the voltage phase θ obtained by the integrator 24, and outputs the calculated voltage command values Vu*, Vv* and Vw* to the PWM-signal generation unit 26. The PWM-signal generation unit 26 compares the voltage command values Vu*, Vv* and Vw* with a carrier signal (reference signal) having an amplitude Vdc/2 at a predetermined frequency, and generates PWM signals UP, VP, WP, UN, VN and WN based on a magnitude relation to each other.

For example, when the voltage command value Vu* is larger than the carrier signal, UP is set to a voltage for turning on the switching element 17 a, and UN is set to a voltage for turning off the switching element 17 d. On the other hand, when the voltage command value Vu* is smaller than the carrier signal, inversely, UP is set to a voltage for turning off the switching element 17 a, and UN is set to a voltage for turning on the switching element 17 d. The same applies to other signals, and VP and VN are determined based on the comparison between the voltage command value Vv* and the carrier signal, and WP and WN are determined based on the comparison between the voltage command value Vw* and the carrier signal.

In a case of a general inverter, because a complementary PWM system is adopted therefor, UP and UN, VP and VN, and WP and WN have an inverse relationship to each other. Therefore, there are eight switching patterns in total.

FIG. 5 is a chart showing eight switching patterns in the first embodiment. In FIG. 5, reference symbols V0 to V7 denote voltage vectors generated in the respective switching patterns. The voltage direction of the respective voltage vectors is indicated by ±U, ±V and ±W (and 0 when the voltage is not generated). Here, “+U” means a voltage for generating a current in the U-phase direction, which flows into the motor 8 via the U-phase and flows out from the motor 8 via the V-phase and the W-phase, and “−U” means a voltage for generating a current in the −U phase direction, which flows into the motor 8 via the V-phase and the W-phase and flows out from the motor 8 via the U-phase. The same applies to ±V and ±W.

The inverter 9 can be caused to output desired voltages by combining the switching patterns shown in FIG. 5 and outputting a voltage vector. At this time, a high frequency voltage can be outputted by changing the phase θ at a high speed.

The voltage command signals Vu*, Vv* and Vw* may be obtained in two-phase modulation, triple harmonic superimposition modulation, space vector modulation, and the like other than Equations (1) to (3).

FIG. 6 is a diagram showing a configuration of the heating determination unit 12 according to the first embodiment.

The heating determination unit 12 controls an operation state (ON/OFF) of the high-frequency-voltage generation unit 11 based on the bus voltage Vdc detected by the bus-voltage detection unit 16 of the inverter 9, the current I detected by the current detection unit 20 of the inverter 9, and the like.

The heating determination unit 12 includes a current comparison unit 27, a voltage comparison unit 28, a temperature detection unit 29, a temperature comparison unit 30, a first logical-product calculation unit 31, a pooling determination unit 32, an elapsed-time measurement unit 33, a time comparison unit 34, a resetting unit 35, a logical-sum calculation unit 36, a second logical-product calculation unit 37, and a heating-amount determination unit 38.

The current comparison unit 27 output “1” with judging that it is a normal state when the current I detected and outputted by the current detection unit 20 is in a state of Imin<I<Imax, but outputs “0” when not in the state.

The Imax is an upper limit of the current, and the Imin is a lower limit of the current. When an excessive positive current equal to or larger than the Imax or an excessive negative current equal to or smaller than the

Imin flows, the current comparison unit 27 determines that the current I is in an abnormal state and outputs “0”, thereby operating to stop heating.

The voltage comparison unit 28 determines that the bus voltage Vdc is in a normal state when the bus voltage Vdc detected by the bus-voltage detection unit 16 is in a state of Vdc_min<Vdc<Vdc_max and outputs “1”, but outputs “0” in other cases.

The Vdc_max is an upper limit of the bus voltage, and the Vdc_min is a lower limit of the bus voltage. In the case of an excessive high bus voltage equal to or higher than the Vdc_max or an excessive low bus voltage equal to or lower than the Vdc_min, the voltage comparison unit 28 determines that the bus voltage is in an abnormal state and outputs “0”, thereby operating to stop heating.

The temperature detection unit 29 detects an inverter temperature Tinv that is a temperature of the voltage application unit 19, a temperature Tc of the compressor 1, and an outside air temperature To.

The temperature comparison unit 30 compares a preset protective temperature Tp_inv of the inverter with the inverter temperature Tinv, and compares a preset protective temperature Tp_c of the compressor 1 with the compressor temperature Tc. The temperature comparison unit 30 determines that a normal operation is currently performed in a state of Tp_inv>Tinv and in a state of Tp_c>Tc and outputs “1”, but outputs “0” in other cases.

In a case of Tp_inv<Tinv, the inverter temperature is high, and in a case of Tp_c<Tc, the winding temperature of the motor 8 in the compressor 1 is high, and so an insulation failure or the like may occur. Therefore, the temperature comparison unit 30 determines that it is dangerous, outputs “0”, and operates to stop the heating. The Tp_c needs to be set, taking into consideration a fact that the compressor 1 has a larger heat capacity than the winding of the motor 8 and the temperature rising speed is lower than that of the winding.

The first logical-product calculation unit 31 outputs a logical product of output values of the current comparison unit 27, the voltage comparison unit 28 and the temperature comparison unit 30. When any one or more of the output values of the current comparison unit 27, the voltage comparison unit 28 and the temperature comparison unit 30 is 0, which indicates an abnormal state, the first logical-product calculation unit 31 outputs “0” to operate to stop the heating.

A method of stopping heating using the current I, the bus voltage Vdc, and the temperatures Tinv and Tc has been explained. However, not all of these values need to be used. Heating may be stopped using a parameter other than these values.

Subsequently, the pooling determination unit 32 determines whether or not a liquid refrigerant is retained in the compressor 1 (the refrigerant is pooled) based on the temperature Tc of the compressor 1 and the outside air temperature To detected by the temperature detection unit 29.

Because the compressor 1 has the largest heat capacity in the refrigeration cycle, and the compressor temperature Tc rises slower compared to the rise of the outdoor air temperature To, the temperature thereof becomes the lowest. Because the refrigerant stays in a place where the temperature is the lowest in the refrigeration cycle, and accumulates as the liquid refrigerant, the refrigerant accumulates in the compressor 1 at the time of temperature rise. In a case of To>Tc, the pooling determination unit 32 determines that the refrigerant stays in the compressor 1, outputs “1” to start heating, and stops the heating when To<Tc.

Control may be executed to start heating when the Tc is in a rising trend or when the To is in a rising trend, and when detection of the Tc or To becomes difficult, the control can be realized using either one of them, thereby enabling to realize highly reliable control.

When both the compressor temperature Tc and the external temperature To can not be detected, heating of the compressor 1 may be impossible. Therefore, the elapsed-time measurement unit 33 measures a time for which the compressor 1 is not heated (Elapse_Time). When a time limit time Limit Time preset by the time comparison unit 34 is exceeded, the elapsed-time measurement unit 33 outputs “1” to start heating of the compressor 1. Because the temperature change in a day is such that temperature rises from morning when the sun rises toward daytime, and temperature drops from evening toward night, temperature rise and drop are repeated in a cycle of roughly 12 hours. For this reason, for example, the Limit Time may be set to about 12 hours.

The Elapse_Time is set to “0” by the resetting unit 35, when the heating of the compressor 1 is executed.

The logical-sum calculation unit 36 outputs a logical sum of output values of the pooling determination unit 32 and the time comparison unit 34. When at least one of the output values of the pooling determination unit 32 and the time comparison unit 34 becomes “1” indicating starting of the heating, the logical-sum calculation unit 36 outputs “1” to start heating of the compressor “1”.

The second logical-product calculation unit 37 outputs a logical product of the output values of the first logical-product calculation unit 31 and the logical-sum calculation unit 36 as an output value of the heating determination unit 12. When the output value is 1, the high-frequency-voltage generation unit 11 is actuated to perform a heating operation of the compressor 1. On the other hand, when the output value is 0, the high-frequency-voltage generation unit 11 is not actuated, and the heating operation of the compressor 1 is not performed, or the operation of the high-frequency-voltage generation unit 11 is stopped to stop the heating operation of the compressor 1.

Because the second logical-product calculation unit 37 outputs the logical product, when a signal “0” for stopping heating of the compressor 1 is being outputted by the first logical-product calculation unit 31, the heating can be stopped even if a signal “1” indicating starting of heating is outputted to the logical-sum calculation unit 36. Therefore, it is possible to realize the heat pump device that can minimize power consumption in a standby mode while ensuring certain reliability.

The pooling determination unit 32 detects a state where a liquid refrigerant is stayed in the compressor 1 based on the compressor temperature Tc and the external temperature To. Furthermore, the heating-amount determination unit 38 determines the amount of the liquid refrigerant retained in the compressor 1 based on the compressor temperature Tc and the external temperature To. The heating-amount determination unit 38 then calculates and outputs the voltage command value Vc required for expelling the refrigerant to outside of the compressor 1 according to the determined amount of the liquid refrigerant. Accordingly, the state where the liquid refrigerant is retained in the compressor 1 can be resolved with the minimum necessary electric power, and the influence on global warming can be reduced with the power consumption being reduced.

An operation of the inverter control unit 10 is explained next.

FIG. 7 is a flowchart showing an operation of the inverter control unit 10 in the first embodiment.

(S1: Heating determining step)

The heating determination unit 12 determines whether to actuate the high-frequency-voltage generation unit 11 by the operation described above during shutdown of the compressor 1.

When the heating determination unit 12 determines that the high-frequency-voltage generation unit 11 should be actuated, that is, when the output value of the heating determination unit 12 is “1” (ON) (YES at S1), the process proceeds to S2 to generate PWM signals for preheating. On the other hand, when the heating determination unit 12 determines that the high-frequency-voltage generation unit 11 should not be actuated, that is, when the output value of the heating determination unit 12 is “0” (OFF) (NO at S1), the heating determination unit 12 determines whether to actuate the high-frequency-voltage generation unit 11 again after a predetermined time has passed.

(S2: Voltage-command-value generating step)

The selection unit 23 selects the voltage command value V* and the rotation-speed command value ω*, and the integrator 24 obtains the voltage phase θ based on the rotation-speed command value ω* selected by the selection unit 23. The voltage-command generation unit 25 calculates the voltage command values Vu*, Vv* and Vw* according to Equations (1) to (3) based on the voltage command value V* selected by the selection unit 23 and the voltage phase θ obtained by the integrator 24, and outputs the calculated voltage command values Vu*, Vv* and Vw* to the PWM-signal generation unit 26.

(S3: PWM-signal generating step)

The PWM-signal generation unit 26 compares the voltage command values Vu*, Vv* and Vw* outputted by the voltage-command generation unit 25 with the carrier signal to obtain the PWM signals UP, VP, WP, UN, VN and WN, and outputs these PWM signals to the inverter 9. Accordingly, the switching elements 17 a to 17 f of the inverter 9 are driven to apply a high-frequency voltage to the motor 8.

By applying the high-frequency voltage to the motor 8, the motor 8 is efficiently heated by iron loss of the motor 8 and copper loss generated by the current flowing in the winding. By the motor 8 being heated, the liquid refrigerant stagnating in the compressor 1 is heated and evaporated, and leaked to outside of the compressor 1.

After a predetermined time has passed, the heating determination unit 12 returns to S1 again, and determines whether further heating is required.

As described above, in the heat pump device 100 according to the first embodiment, when the liquid refrigerant is stagnating in the compressor 1, the high-frequency voltage is applied to the motor 8, so that the motor 8 can be efficiently heated while restraining noise. Accordingly, the refrigerant retained in the compressor 1 can be efficiently heated, and the retained refrigerant can be leaked to outside of the compressor 1.

When the high-frequency voltage having a frequency equal to or higher than an operation frequency at the time of a compression operation is applied to the motor 8, a rotor in the motor 8 can not follow the frequency, and any rotations or vibrations are not generated. Therefore, at S2, the selection unit 23 had better output a rotation-speed command value ω* equal to or higher than the operation frequency at the time of the compression operation.

Generally, the operation frequency at the time of the compression operation is 1 kHz at most. Therefore, a high frequency voltage having a frequency equal to or larger than 1 kHz only has to be applied to the motor 8. When a high frequency voltage having a frequency equal to or higher than 14 kHz is applied to the motor 8, vibration sound of an iron core of the motor 8 approaches nearly an upper limit of an audible frequency, so that there is an effect for reducing noise. To this end, for example, the selection unit 23 outputs the rotation-speed command value ω* for leading to a high frequency voltage of about 20 kHz.

However, when the frequency of the high frequency voltage exceeds the maximum rated frequency of the switching elements 17 a to 17 f, a load or power supply short-circuit may occur due to breakage of the switching elements 17 a to 17 f, and it can lead to generation of smoke or fire. For this reason, it is desired to set the frequency of the high-frequency voltage to be equal to or lower than the maximum rated frequency in order to ensure reliability.

Furthermore, to achieve a high efficiency, a motor having an IPM (Interior Permanent Magnet) structure or a concentrated winding motor having a small coil end and a low winding resistance has been widely used for the recent compressor motor for a heat pump device. The concentrated winding motor has a small winding resistance and a small amount of heat generation due to copper loss, and thus a large amount of current needs to be caused to flow to the winding. If a large amount of current is caused to flow to the winding, then the current flowing to the inverter 9 also increases, thereby increasing inverter loss.

Therefore, if heating by applying the high-frequency voltage described above is performed, then an inductance component by the high frequency increases, thereby increasing winding impedance. Accordingly, although the current flowing to the winding decreases and the copper loss is reduced, iron loss due to the application of the high-frequency voltage occurs corresponding to the amount of copper loss, thereby enabling to perform efficient heating. Furthermore, because the current flowing to the winding decreases, the current flowing to the inverter also decreases, thereby enabling to reduce the loss of the inverter 9 and perform more efficient heating.

If heating by applying the high-frequency voltage described above is performed, when the compressor is based on a motor having the IPM structure, a rotor surface where high-frequency magnetic fluxes interlink with each other also becomes a heat generating portion. Therefore, increase in an area contacting the refrigerant and prompt heating of the compression mechanism can be realized, thereby enabling to perform efficient heating of the refrigerant.

At present, generally, the mainstream trend is to use silicon (Si) as a material of a semiconductor for the switching elements 17 a to 17 f that constitute the inverter 9 and the reflux diodes 18 a to 18 f that are connected to the respective switching elements 17 a to 17 f in parallel. However, instead of this type of semiconductor, a wide bandgap semiconductor whose material is silicon carbide (SiC), gallium nitride (GaN) or diamond may be used.

Switching elements and diode elements made from such a wide bandgap semiconductor have a high voltage resistance and a high allowable current density. Therefore, downsizing of the switching elements and diode elements is possible, and by using these downsized switching elements and diode elements, downsizing of a semiconductor module having these elements incorporated therein can be realized.

The switching elements and the diode elements made from such a wide bandgap semiconductor have a high heat resistance. Accordingly, downsizing of a radiator fin of a heat sink and air cooling of a water cooling part can be realized, thereby enabling further downsizing of the semiconductor module.

Furthermore, the switching elements and the diode elements made from such a wide bandgap semiconductor have low power loss. Therefore, the switching elements and the diode elements can be made to have a high efficiency, thereby enabling to make the semiconductor module highly efficient.

While it is desired that both the switching elements and the diode elements are made from a wide bandgap semiconductor, it is also sufficient that either the switching or diode elements are made from a wide bandgap semiconductor, and even in this case, effects described in the present embodiment can be achieved.

Besides, identical effects can be produced by using a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) having a super junction structure that is known as a highly efficient switching element.

In a compressor having a scroll mechanism, high-pressure relief of a compression chamber is difficult. Therefore, there is a high possibility of causing breakage of the compression mechanism due to an excessive stress applied to the compression mechanism in a case of liquid compression, as compared to a compressor of other systems. However, in the heat pump device 100 according to the first embodiment, efficient heating of the compressor 1 is possible, and stagnation of a liquid refrigerant in the compressor 1 can be suppressed. Accordingly, liquid compression can be prevented, the heat pump device 100 is beneficial even when a scroll compressor is used as the compressor 1.

Furthermore, in the case of a heating device having a frequency of 10 kHz and an output exceeding 50W, the heating device may be subjected to the restriction of laws and regulations. For this reason, it may as well be admitted that an amplitude of the voltage command value is adjusted so as not to exceed 50W in advance, and/or feedback control is executed with detecting the flowing current and the voltage so as to be 50W or less.

The inverter control unit 10 is configured by a CPU (Central Processing Unit), a DSP (Digital Signal Processor), a microcomputer, an electronic circuit or the like.

Second Embodiment

In a second embodiment, a method of generating a high frequency voltage is described.

In a case of a general inverter, a carrier frequency, that is a frequency of a carrier signal, has an upper limit that is determined by a switching speed of switching elements of the inverter. Therefore, it is difficult to output a high frequency voltage having a frequency equal to or higher than the carrier frequency. In a case of a general IGBT (Insulated Gate Bipolar Transistor), the upper limit of the switching speed is about 20 kHz.

When the frequency of the high frequency voltage becomes about 1/10 of the carrier frequency, an adverse effect may occur such that the waveform output accuracy of the high frequency voltage deteriorates and DC components are superposed on the high frequency voltage. When the carrier frequency is set to 20 kHz in view of the above, if the frequency of the high frequency voltage is set equal to or lower than 2 kHz that is 1/10 of the carrier frequency, then the frequency of the high frequency voltage is in an audible frequency domain, and so it is a concern that noise is increased.

FIG. 8 is a diagram showing a configuration of the inverter control unit 10 according to the second embodiment.

The inverter control unit 10 according to the second embodiment is the same as the inverter control unit 10 according to the first embodiment shown in FIG. 3, except that the high-frequency-voltage generation unit 11 includes an addition unit 39 that adds a phase ηp or a phase θn switched by the selection unit 23 to the reference phase θf to obtain the voltage phase θ, instead of the integrator 24 (see FIG. 3). Therefore, constituent elements identical to those of the first embodiment are denoted by the same reference signs and explanations thereof will be omitted, and only different points are explained.

In the first embodiment, the rotation-speed command value ω* is integrated by the integrator 24 to obtain the voltage phase θ. On the other hand, in the second embodiment, the selection unit 23 (phase switching unit) alternately switches between two types of voltage phases, the phase ηp and the phase θn that is different from the phase ηp substantially by 180 degrees. The addition unit 39 then adds the phase ηp or θn selected by the selection unit 23 to the reference phase θf and designates the obtained phase as the voltage phase θ.

In the explanations below, it is assumed that ηp=0 [degree], and θn=180 [degrees].

An operation of the inverter control unit 10 is explained next.

Except for the operation of S2 shown in FIG. 7, operations of the inverter control unit 10 are the same as those of the inverter control unit 10 according to the first embodiment. Therefore, explanations thereof will be omitted.

At S2, the selection unit 23 switches between the phases ηp and θn alternately at the timing of either a top (peak) or bottom (valley) of a carrier signal or at the timings of the top and bottom of the carrier signal. The addition unit 39 adds the phase ηp or phase θn selected by the selection unit 23 to the reference phase θf, designates the obtained phase as the voltage phase θ, and outputs the voltage phase θ to the voltage-command generation unit 25. The voltage-command generation unit 25 obtains the voltage command values Vu*, Vv* and Vw* according to Equations (1) to (3) using the voltage phase θ and the voltage command value V*, and outputs the voltage command values Vu*, Vv* and Vw* to the PWM-signal generation unit 26.

Because the selection unit 23 switches between the phases ηp and θn at the timing of the top or bottom, or at the timings of the top and bottom of the carrier signal, the PWM signal synchronized with the carrier signal can be outputted.

FIG. 9 is a timing chart when the phase ηp and the phase θn are alternately switched by the selection unit 23 at timings of a top and a bottom of a carrier signal. Because the UP, VP and WP are opposite in ON/OFF state to UN, VN and WN, respectively and when the state of one signal is ascertained, the other one can be ascertained, only UP, VP and WP are described here. It is assumed here that θf=0 [degree].

In this case, a PWM signal changes as shown in FIG. 9. The voltage vector changes in order of V0 (UP=VP=WP=0), V4 (UP=1, VP=WP=0), V7 (UP=VP=WP=1), V3 (UP=0, VP=WP=1), V0 (UP=VP=WP=0), and so on.

FIG. 10 is an explanatory diagram of a change of the voltage vector shown in FIG. 9. In FIG. 10, it is indicated that the switching element 17 surrounded by a broken line is ON, and the switching element 17 not surrounded by a broken line is OFF.

As shown in FIG. 10, at the time of applying the V0 vector and the V7 vector, lines of the motor 8 are short-circuited, and a de-energized section is formed in which any voltage is not outputted. In this case, the energy accumulated in the inductance of the motor 8 becomes a current, and the current flows in the short circuit. At the time of applying the V4 vector, a current (current of +Iu current) flows in the direction of the U-phase, in which the current flows into the motor 8 via the U-phase and flows out from the motor 8 via the V-phase and the W-phase, and at the time of applying the V3 vector, a current (current of −Iu) flows to the winding of the motor 8 in the direction of the −U phase, in which the current flows into the motor 8 via the V-phase and the W-phase and flows out from the motor 8 via the U-phase. That is, the current flows to the winding of the motor 8 at the time of applying the V4 vector in the opposite direction to that at the time of applying the V3 vector and vice versa. Because the voltage vector changes in order of V0, V4, V7, V3, V0, and so on, the current of +Iu and the current of −Iu flow to the winding of the motor 8 alternately. Particularly, as shown in FIG. 9, because the V4 vector and the V3 vector appear during one carrier cycle (1/fc), an AC voltage synchronized with a carrier frequency fc can be applied to the winding of the motor 8.

Because the V4 vector (the current of +Iu) and the V3 vector (the current of −Iu) are alternately output, forward and reverse torques are switched instantaneously. Therefore, because the torque is compensated, the voltage application is possible, while suppressing vibrations of the rotor.

FIG. 11 is a timing chart when the phase ηp and the phase θn are alternately switched by the selection unit 23 at a timing of a bottom of a carrier signal.

In this case, the PWM signal changes as shown in FIG. 11. The voltage vector changes to V0, V4, V7, V7, V3, V0, V0, V3, V7, V7, V4, V0, and so on in this order. Because the V4 vector and the V3 vector appear during two carrier cycles, an AC voltage having a frequency half the carrier frequency can be applied to the winding of the motor 8.

FIG. 12 is an explanatory diagram of a rotor position (a stop position of the rotor) of an IPM motor. A rotor position φ of the IPM motor is expressed here by the size of an angle by which the direction of the N pole of the rotor deviates from the U-phase direction.

FIG. 13 is a graph showing current change according to a rotor position. In the case of the IPM motor, the winding inductance depends on the rotor position. Therefore, the winding impedance expressed by a product of an electric angle frequency w and an inductance value fluctuates according to the rotor position. Accordingly, even if the same voltage is applied, a current flowing to the winding of the motor 8 changes depending on the rotor position, and a heating amount changes. As a result, a large amount of power may be consumed to obtain the required heating amount, depending on the rotor position.

Therefore, the reference phase θf is changed with a lapse of time to apply a voltage to the rotor evenly.

FIG. 14 is an illustration showing applied voltages when the reference phase θf is changed with a lapse of time.

The reference phase θf is changed every 45 degrees with a lapse of time, at 0 degree, 45 degrees, 90 degrees, 135 degrees, and so on. When the reference phase θf is 0 degree, the phase θ of the voltage command value becomes 0 degree and 180 degrees. When the reference phase θf is 45 degrees, the phase θ of the voltage command value becomes 45 degrees and 225 degrees. When the reference phase θf is 90 degrees, the phase θ of the voltage command value becomes 90 degrees and 270 degrees. When the reference phase θf is 135 degrees, the phase θ of the voltage command value becomes 135 degrees and 315 degrees.

That is, the reference phase θf is initially set to 0 degree, and the phase θ of the voltage command value is switched between 0 degree and 180 degrees in synchronization with a carrier signal for a predetermined time. Thereafter, the reference phase θf is switched to 45 degrees, and the phase θ of the voltage command value is switched between 45 degrees and 225 degrees in synchronization with the carrier signal for the predetermined time. Subsequently, the reference phase θf is switched to 90 degrees and so on. In this manner, the phase θ of the voltage command value is switched between 0 degree and 180 degrees, 45 degrees and 225 degrees, 90 degrees and 270 degrees, 135 degrees and 315 degrees, and so on for each predetermined time.

Accordingly, because an energization phase of a high-frequency AC voltage changes with a lapse of time, the influence of inductance characteristics according to a rotor stop position can be eliminated, and the compressor 1 can be heated uniformly, regardless of the rotor position.

FIG. 15 is a chart representing currents flowing to the respective U-, V- and W-phases of the motor 8 when the reference phase θf is 0 degree (0 degree in the U-phase (V4) direction), 30 degrees, and 60 degrees.

When the reference phase θf is 0 degree, as shown in FIG. 9, only one other voltage vector (voltage vector in which, of the switching elements 17 a to 17 f, one switching element on the positive voltage side and two switching elements on the negative voltage side, or two switching elements on the positive voltage side and one switching element on the negative voltage side become an ON state) is generated between V0 and V7. In this case, the current waveform becomes a trapezoidal shape and becomes a current having less harmonic components.

However, when the reference phase θf is 30 degrees, two different voltage vectors are generated between V0 and V7. In this case, the current waveform is distorted, and the current has plenty of harmonic components. The distortion of the current waveform may cause adverse effects including motor noise, motor shaft vibrations, and the like.

When the reference phase θf is 60 degrees, only one other voltage vector is generated between V0 and V7, as in the case of the reference phase θf being 0 degree. In this case, the current waveform becomes a trapezoidal shape and the current has less harmonic components. In this manner, when the reference phase θf is n times (n is an integer equal to or larger than 0) of 60 degrees, because the voltage phase θ becomes a multiple of 60 degrees (here, ηp=0 [degree], θn=180 [degrees]), only one other voltage vector is generated between V0 and V7. Meanwhile, when the reference phase θf is other than n times of 60 degrees, because the voltage phase θ does not become a multiple of 60 degrees, two other voltage vectors are generated between V0 and V7. If two other voltage vectors are generated between V0 and V7, the current waveform is distorted, and the current has plenty of harmonic components, thereby leading to possibility of causing adverse effects including motor noise, motor shaft vibrations, and the like. Therefore, it is desired to change the reference phase θf at 60-degree intervals of 0 degree, 60 degrees, and so on.

As described above, in the heat pump device 100 according to the second embodiment, two types of phases of a phase θ1 and a phase θ2 different from the phase θ1 substantially by 180 degrees are switched alternately, in synchronization with the carrier signal, and then onf of them is used as a phase of the voltage command value. Accordingly, the high frequency voltage synchronized with the carrier frequency can be applied to the winding of the motor 8.

In the heat pump device 100 according to the second embodiment, the reference phase θf is changed with a lapse of time. Accordingly, because the energization phase of the high-frequency AC voltage changes with the lapse of time, the compressor 1 can be heated uniformly, regardless of the rotor position.

Third Embodiment

In a third embodiment, there is described a method of maintaining the heating amount of the compressor constant regardless of the influences of production tolerance and environment variations when the high-frequency AC voltage is generated.

FIG. 16 is a diagram showing a configuration of the inverter control unit 10 according to the third embodiment.

The inverter control unit 10 according to the third embodiment is the same as the inverter control unit 10 according to the second embodiment shown in FIG. 8, except for including a high-frequency-current detection unit 40. Therefore, constituent elements identical to those of the above embodiments are denoted by like reference signs and explanations thereof will be omitted, and only different points are explained.

In the second embodiment, the heating determination unit 12 is operated using the current value I detected by the current detection unit 20 as an input. In contrast, in the third embodiment, the high-frequency-current detection unit 40 acquires the current value I detected by the current detection unit 20 at a predetermined timing, and outputs the current value I as a high-frequency current value Ih. Then, the high-frequency current value Ih_outputted by the high-frequency-current detection unit 40 is used as an input of the heating determination unit 12 to operate the heating determination unit 12.

The timing at which the high-frequency-current detection unit 40 acquires the current value I detected by the current detection unit 20 is explained.

FIG. 17 is a chart in which a voltage and a current of the motor 8 are indicated on the timing chart shown in FIG. 9.

Because the motor voltage becomes positive in a section of the V4 vector in the motor current waveform, the motor current flows from the negative side to the positive side. Subsequently, in a section of the V7 vector, the motor voltage becomes zero and it operates to cause short-circuit between the lines of the motor 8, and thus the energy accumulated in the inductance of the motor 8 attenuates with a time constant determined by a resistance component and an inductance component of the motor 8. Thereafter, because the motor voltage becomes negative in a section of the V3 vector, the motor current flows from the positive side to the negative side, and it operates to cause short-circuit again between the lines of the motor 8 in a section of the V0 vector, so that the energy attenuates with the time constant described above.

The time constant described above is about several milliseconds, and is sufficiently long as compared with a cycle of 50 microseconds when the output frequency is 20 kHz. Accordingly, in the sections of the V0 vector and the V7 vector, it operates to keep the current generated in the sections of V4 vector and the V3 vector.

Because the current detection unit 20 detects a current flowing to the motor 8, the current detection unit 20 can detect the current equivalent to the current actually flowing to the motor 8. However, a CPU (Central Processing Unit), a DSP (Digital Signal Processor), a microcomputer, or the like is generally used for the inverter control unit 10. For this reason, the inverter control unit 10 performs A/D conversion regarding detection of the current, in which the current is converted to a voltage by a current sensor or the like and then is converted from an analog value to a digital value. Generally, these conversions take time. Particularly, when the inverter control unit 10 is constituted by an inexpensive CPU or the like, a longer time is required. Accordingly, accurate current detection is difficult for the inverter control unit 10 when the current has a high frequency.

Generally, it often happens that the inverter control unit 10 detects the current once in one cycle of a carrier signal or once from the bottom to the top and once from the top to the bottom of the carrier signal. Therefore, if the current is detected at a wrong timing, a desired current value (generally, a peak value) can not be detected.

Therefore, the high-frequency-current detection unit 40 designates a portion where the current is comparatively stable near the peak (a portion indicated by a broken line on the output current of the current detection unit 20 in FIG. 17) as a current detectable section (detection section), and acquires the current value detected by the current detection unit 20 at this timing. Accordingly, the high-frequency-current detection unit 40 can detect an approximate peak value of the motor current.

The current detectable section is a section from immediately before the end of the output of the motor voltage to immediately after the start of the output of the motor voltage through the zero section of the motor voltage. That is, in FIG. 17, the current detectable section lasts from immediately before the end of the output of the V4 vector to immediately after the start of the output of the V3 vector through the sections of the V7 vector, and from immediately before the end of the output of the V3 vector to the immediately after the start of the output of the V4 vector through the sections of the V0 vector.

A specific one phase of the motor 8 is explained here. However, a high-frequency current value of multiple phases can be detected in the same manner. If two phases of the three phases (U, V and W phases) can be detected, the current of the remaining one phase, which has not been detected, can be determined by the Kirchhoff's laws in which the sum of the currents Iu, Iv and Iw flowing to the U, V and W phases is 0.

When it is difficult to measure the detection timing in the current detectable section, the high-frequency current value may be detected with a very short interval as compared with the cycle, such as 0 [μs] later or 5 [μs] later, using the top of the carrier signal as a reference, for example and the currents for several cycles of the carrier signal may be averaged. In this way, although some error occurs, the value of the high-frequency current can be reliably detected. By averaging the positive values and the negative values separately, the positive current value and the negative current value can be acquired.

FIG. 18 is a diagram showing a configuration of the heating determination unit 12 according to the third embodiment. The heating determination unit 12 according to the third embodiment is the same as the heating determination unit 12 according to the first embodiment shown in FIG. 6, except for including a heating-amount adjustment unit 41. Therefore, elements identical to those of the first embodiment are denoted by the same reference signs and explanations thereof will be omitted, and only different points are explained.

According to the second embodiment, the heating-amount determination unit 38 calculates and outputs the voltage command value Vc required for letting out the refrigerant to outside of the compressor 1 according to the specified amount of the liquid refrigerant. On the other hand, according to the third embodiment, the heating-amount determination unit 38 calculates the power (the amount of heat) required for letting out the refrigerant to outside of the compressor 1 according to the specified amount of the liquid refrigerant. Then, the heating-amount adjustment unit 41 calculates and outputs a voltage command value Vc that can acquire the calculated power based on the high-frequency current value Ih.

FIG. 19 is a graph showing a relation between power required for causing the liquid refrigerant stayed in the compressor 1 to leak outside and a current value required for acquiring the power.

The heating-amount adjustment unit 41 determines the relation between the required power and the current value required for acquiring the power as shown in FIG. 19 beforehand, and stores the relation in a memory. Then, the heating-amount adjustment unit 41 calculates the voltage command value Vc so that the current value required for acquiring the power calculated by the heating-amount determination unit 38 matches with the high frequency current Ih.

Accordingly, as shown in FIG. 13, the heating amount of the compressor 1 can be maintained constant, regardless of the influences of production tolerance and environment variations.

As shown in FIG. 13, when the reference phase θf is fixed, there are a rotor position φ where the current easily flows, and another rotor position φ where the current difficultly flows. Also in the case where the rotor position φ is fixed and the reference phase θf is variable, there are a reference phase θf in which the current easily flows, and another reference phase θf in which the current difficultly flows. In the rotor position φ or in the reference phase θf where the current easily flows, a large current can be caused to flow with a less voltage, and therefore the compressor 1 can be efficiently heated.

In the circumstances, the rotor position φ or the reference phase θf is changed, and the high-frequency current Ih for each rotor position φ or reference phase θf is ascertained, thereby driving the motor in the rotor position φ or the reference phase θf where the current becomes the largest. Accordingly, the compressor 1 can be efficiently heated.

According to the second embodiment, as shown in FIG. 8, the voltage-command generation unit 25 generates the voltage command values Vu*, Vv* and Vw* using the voltage command value V* and the voltage phase θ as inputs thereof. According to the third embodiment, as shown in FIG. 16, the high-frequency-current detection unit 40 calculates and outputs a DC offset value Ih_offset superposed on the current based on the acquired high-frequency current value Ih. The voltage-command generation unit 25 then uses the DC offset value Ih_offset as an input thereof in addition to the voltage command value V* and the voltage phase θ, to generate the voltage command values Vu*, Vv* and Vw*.

FIG. 20 is an explanatory chart of a process when a DC offset is superposed on a motor current. In FIG. 20, there is shown a situation in which the DC offset is initially superposed on the motor current, but the DC offset is corrected so as to be gradually removed by adjusting the voltage command values Vu*, Vv* and Vw*.

The inverter control unit 10 is generally constituted by a discrete system typified by a CPU, DSP or microcomputer, and a computing error may be non-negligible. Therefore, as shown in FIG. 20, the DC offset may be superimposed on the motor current. If a high-frequency voltage is applied in a state with the DC offset being superimposed thereon, a loss of the switching element constituting the inverter 9 is large and heat is generated. Therefore, if the operation is continued for a long time, a thermal fracture may occur. Furthermore, in the recent design of the motor 8, the motor is designed to have a low winding resistance in order to reduce a loss due to the winding resistance. In this situation, if a DC offset occurs even slightly, an excessive current may flow due to the DC current.

Therefore, the high-frequency-current detection unit 40 detects a positive peak value Ihp[n] and a negative peak value Ihn[n] of the high-frequency current. The high-frequency-current detection unit 40 calculates a mean value of detection values Ihp[1] and Ihn[1] in the first round as a DC offset amount Ih_offset.

The voltage-command generation unit 25 adjusts the voltage command values Vu*, Vv* and Vw* based on the calculated offset amount Ih_offset. For example, when the DC offset in the positive direction is superposed on the U-phase current, the voltage-command generation unit 25 adjusts the voltage command value Vu* to be displaced gradually in the negative direction. On the other hand, when the DC offset in the negative direction is superposed on the U-phase current, the voltage-command generation unit 25 adjusts the voltage command value Vu* to be displaced gradually in the positive direction. The same holds true for the V phase and the W shape. Accordingly, the control can be made so that the DC offset amount becomes 0.

Variations in the peak value of the current may occur due to an influence of noise or the like. Therefore, the mean value of the detection values Ihp[1] and Ihn[1] in the first round is not be set to the DC offset amount Ih_offset, and the DC offset amount Ih_offset may be calculated using the detection values from the first round to the nth round (n is an integer equal to or larger than 2). For example, the detection values from the first round to the nth round (n is an integer equal to or larger than 2) may be averaged by use of a method generally and widely used, such as an LPF (Low Pass Filter) or a moving average so that the variation becomes small.

In the above explanations, it is explained to detect the peak value (high-frequency current value Ih) of the motor current. However, the mean value of the motor current can be calculated based on the peak value of the motor current.

As shown in FIG. 17, the current polarity of the motor current changes in the sections of the V4 vector and the V3 vector, and the operation is made to keep the peak value of the motor current in the sections of the V0 vector and the V7 vector. The current waveform has substantially a trapezoidal shape. Therefore, if an upper base is the length of the section of the V7 vector, a lower base is a half cycle of the carrier, and the height is the high-frequency current Ih detected by the high-frequency-current detection unit 40, then an area of the current waveform can be determined by a formula for calculating the area of a trapezoid. This area is divided by the time to obtain a mean value of the area with respect to the time, thereby enabling to obtain the mean value of the motor current.

More accurate control may be performed using the mean value of the motor current instead of the peak value of the motor current. For example, the heating-amount adjustment unit 41 may calculate the voltage command value Vc so that the current value required for acquiring the power calculated by the heating-amount determination unit 38 matches with the mean value of the motor current.

For example, when the single-phase motor 8 is considered, the motor 8 has a circuit of a winding resistance R and a winding inductance L. Therefore, the winding resistance R of the motor 8 can be estimated based on V=(R+jωL)I using the high-frequency current Ih detected by the high-frequency-current detection unit 40. The winding resistance R changes linearly due to temperature change and there is a tendency such that the winding resistance R becomes high when the winding temperature is high. For example, the value of the winding resistance R at the time of the reference temperature being 20° C. is stored, and the current winding temperature can be estimated from a difference between the stored value and the estimated winding resistance R.

For example, the heating determination unit 12 may determine whether or not to perform the heating operation (ON/OFF) based on the relation between the external temperature and the estimated winding temperature, or may increase the voltage command value Vc to be outputted when the estimated winding temperature is low. By performing such control, the liquid refrigerant stayed in the compressor 1 can be reliably leaked outside. When the estimated winding temperature becomes extremely high (for example, 100° C. or higher), it is considered that this situation is dangerous, and the ON/OFF state, that is the output of the heating determination unit 12, is to be OFF. In this way, the heat pump device 100 having high reliability can be realized.

In the heat pump device 100 according to the third embodiment, as described above, a value of the current flowing to the inverter 9 is detected in the current detectable section. Accordingly, the peak value of the current can be detected accurately. By detecting the peak value of the current accurately, the heating amount of the compressor 1 can be maintained constant. Furthermore, other various types of control can be accurately performed by detecting the peak value of the current accurately. Therefore, the heat pump device 100 having high reliability can be achieved.

Specifically, even when an inexpensive product is used for the CPU or the like constituting the inverter control unit 10, the peak value of the current can be accurately detected. Accordingly, the heat pump device 100 can be provided at low cost.

Fifth Embodiment

In the first to third embodiments, the high-frequency current Ih is detected from the current flowing from the inverter 9 to the motor 8. In a fourth embodiment, a configuration of detecting the high-frequency current Ih from the DC current of the inverter 9 is explained.

FIG. 21 is a diagram showing a configuration of the inverter 9 according to the fourth embodiment.

The inverter 9 according to the fourth embodiment is the same as the inverter 9 according to the first embodiment shown in FIG. 2, except for including a DC-current detection unit 42 instead of the current detection unit 20. Therefore, constituent elements identical to those of the first embodiment are denoted by the same reference signs and explanations thereof will be omitted, and only different points are explained.

The DC-current detection unit 42 is provided in a portion where the inverter portions (serial connection parts) in the inverter 9 are connected in parallel. The DC-current detection unit 42 detects the DC current of the inverter 9 and outputs the DC current to the inverter control unit 10.

FIG. 22 is a chart in which a voltage and a current of the motor 8 and a current detected by the DC-current detection unit 42 are indicated on the timing chart shown in FIG. 9.

As explained in the third embodiment, the motor voltage becomes zero in the sections of the V0 vector and the V7 vector of the switching pattern shown in FIG. 5, and it operates to cause short-circuit between the lines of the motor 8. Therefore, the current does not flow to the DC-current detection unit 42. Accordingly, the current flows to the DC-current detection unit 42 only in the sections of the V1 to V6 vectors.

Therefore, the high-frequency-current detection unit 40 sets the current detectable section immediately after the start of the output of the motor current or immediately before the end of the output of the motor current, and acquires the current value detected by the DC-current detection unit 42 at this timing. Accordingly, the high-frequency-current detection unit 40 can detect an approximate peak value of the motor current.

In other words, the current detectable section resides immediately after the end of the zero section of the motor voltage or immediately before the start of the zero section of the motor voltage. That is, in FIG. 22, the current detectable section resides immediately after the start of the output of the V4 vector and the V3 vector (immediately after the end of the section of the V0 or V7 vector), or immediately before the end of the output of the V4 vector and the V3 vector (immediately before the start of the section of the V0 or V7 vector).

In the heat pump device 100 according to the fourth embodiment, as described above, the DC-current detection unit 42 is used instead of the current detection unit 20. In this case, the current can be detected by a single sensor. Therefore, the heat pump device 100 that realizes reliability improvement and cost reduction by reducing the number of parts can be acquired.

Fifth Embodiment

In the fourth embodiment, the high-frequency current Ih is detected from the DC current of the inverter 9. In a fifth embodiment, a configuration of detecting the high-frequency current Ih from the current flowing to the inverter portion of the inverter 9 is explained.

FIG. 23 is a diagram showing a configuration of the inverter 9 according to the fifth embodiment.

The inverter 9 according to the fifth embodiment is the same as the inverter 9 according to the fourth embodiment shown in FIG. 21, except for including an inverter-current detection unit 43 instead of the DC-current detection unit 42. Therefore, constituent elements identical to those of the fourth embodiment are denoted by the same reference signs and explanations thereof will be omitted, and only different points are explained.

The inverter-current detection unit 43 is provided immediately below the switching elements 17 d, 17 e and 17 f on the negative voltage side of the inverter portion in the inverter 9. Then, the inverter-current detection unit 43 detects the current flowing to the inverter portion, and outputs the result to the inverter control unit 10.

FIG. 24 is a chart in which a voltage and a current of the motor 8 and a current detected by the inverter-current detection unit 43 are indicated on the timing chart shown in FIG. 9.

The high-frequency-current detection unit 40 designates a portion where the current is comparatively stable near the peak (a portion indicated by a broken line on the output current of the inverter-current detection unit 43 in FIG. 24) as the current detectable section, and acquires the current value detected by the inverter-current detection unit 43 at this timing. Accordingly, the high-frequency-current detection unit 40 can detect an approximate peak value of the motor current.

The current detectable section resides immediately after the start of the output of the motor voltage (immediately after the end of the zero section of the motor voltage), and in a section from immediately before the end of the output of the motor voltage (immediately before the start of the zero section of the motor voltage) to the end of the zero section of the motor voltage. That is, in FIG. 24, the current detectable section resides immediately after the start of the output of the V3 vector, and resides from immediately before the end of the output of the V3 vector to the end of the sections of the V0 vector.

A specific one phase of the motor 8 is explained here. However, a high-frequency current value of multiple phases can be detected in the same manner. If two phases of the three phases (U, V and W phases) can be detected, the current of the remaining one phase, which has not been detected, can be determined by the Kirchhoff's laws in which the sum of the currents Iu, Iv and Iw flowing to the U, V and W phases is 0.

As described above, in the heat pump device 100 according to the fifth embodiment, the inverter-current detection unit 43 provided immediately below the switching elements on the negative voltage side is used instead of the DC-current detection unit 42. Generally, one side of the inverter-current detection unit 43 is grounded. Therefore, the flowing current can be detected based on the resistance value and a difference in potential by installing a resistor or the like to detect the difference in potential across the resistor without using any special sensor. Accordingly, the heat pump device 100 that realizes cost reduction can be achieved.

Sixth Embodiment

In a sixth embodiment, one example of a circuit configuration of the heat pump device 100 is explained.

For example, in FIG. 1, there is shown the heat pump device 100 in which the compressor 1, the four-way valve 2, the heat exchanger 3, the expansion mechanism 4 and the heat exchanger 5 are sequentially connected by the piping. In the sixth embodiment, the heat pump device 100 having a more specific configuration is explained.

FIG. 25 is a circuit configuration diagram of the heat pump device 100 according to the sixth embodiment.

FIG. 26 is a Mollier diagram of a state of the refrigerant of the heat pump device 100 shown in FIG. 25. In FIG. 26, a specific enthalpy is indicated on a horizontal axis, and a refrigerant pressure is indicated on a vertical axis.

In the heat pump device 100, a compressor 51, a heat exchanger 52, an expansion mechanism 53, a receiver 54, an internal heat exchanger 55, an expansion mechanism 56, and a heat exchanger 57 are sequentially connected by piping, and the heat pump device 100 includes a main refrigerant circuit 58 through which the refrigerant circulates. In the main refrigerant circuit 58, a four-way valve 59 is provided on a discharge side of the compressor 51, so that a circulation direction of the refrigerant can be switched. A fan 60 is provided near the heat exchanger 57. The compressor 51 is the compressor 1 explained in the embodiment described above, and includes the motor 8 driven by the inverter 9 and the compression mechanism 7.

Furthermore, the heat pump device 100 includes an injection circuit 62 that connects from between the receiver 54 and the internal heat exchanger 55 to an injection pipe of the compressor 51 by the piping. An expansion mechanism 61 and the internal heat exchanger 55 are sequentially connected to the injection circuit 62.

A water circuit 63 in which water is circulated is connected to the heat exchanger 52. A device that uses water from a hot water dispenser, a radiator, a radiator for floor heating, or the like is connected to the water circuit 63.

An operation of the heat pump device 100 at the time of a heating operation is explained first. At the time of the heating operation, the four-way valve 59 is set in a direction of a solid line. The heating operation includes not only heating used for air conditioning but also hot-water supply for applying heat to water to make hot water.

A gas-phase refrigerant (at a point 1 in FIG. 26), which has become a refrigerant having a high temperature and a high pressure in the compressor 51, is discharged from the compressor 51, and heat exchanged by the heat exchanger 52, which is a condenser and a radiator, to be liquefied (at a point 2 in FIG. 26). At this time, water circulating in the water circuit 63 is heated by heat radiated from the refrigerant, and used for heating and hot-water supply.

The liquid-phase refrigerant liquefied by the heat exchanger 52 is pressure-reduced by the expansion mechanism 53, and becomes a gas-liquid two-phase state (at a point 3 in FIG. 26). The refrigerant, which has become the gas-liquid two-phase state in the expansion mechanism 53, is heat exchanged with the refrigerant sucked into the compressor 51 by the receiver 54, and is cooled and liquefied (at a point 4 in FIG. 26). The liquid-phase refrigerant liquefied by the receiver 54 is branched to the main refrigerant circuit 58 and the injection circuit 62 to flow therein.

The liquid-phase refrigerant flowing in the main refrigerant circuit 58 is heat exchanged with the refrigerant flowing in the injection circuit 62, which is pressure-reduced by the expansion mechanism 61 and has become the gas-liquid two-phase state, by the internal heat exchanger 55 and is further cooled (at a point 5 in FIG. 26). The liquid-phase refrigerant cooled by the internal heat exchanger 55 is pressure-reduced by the expansion mechanism 56 and becomes the gas-liquid two-phase state (at a point 6 in FIG. 26). The refrigerant, which has become the gas-liquid two-phase state in the expansion mechanism 56, is heat exchanged with ambient air by the heat exchanger 57, which is an evaporator, and is heated (at a point 7 in FIG. 26). The refrigerant heated by the heat exchanger 57 is further heated by the receiver 54 (at a point 8 in FIG. 26), and is sucked into the compressor 51.

On the other hand, as described above, the refrigerant flowing in the injection circuit 62 is pressure-reduced by the expansion mechanism 61 (at a point 9 in FIG. 26), and heat exchanged by the internal heat exchanger 55 (at a point 10 in FIG. 26). A refrigerant (injection refrigerant) in the gas-liquid two-phase state, which has been subjected to thermal exchange by the internal heat exchanger 55, flows into inside of the compressor 51 from the injection pipe of the compressor 51 keeping in the gas-liquid two-phase state.

In the compressor 51, the refrigerant sucked in from the main refrigerant circuit 58 (at the point 8 in FIG. 26) is compressed up to an intermediate pressure and heated (at a point 11 in FIG. 26). The injection refrigerant (at the point 10 in FIG. 26) joins the refrigerant compressed to the intermediate pressure and heated (at the point 11 in FIG. 26), thereby decreasing the temperature (at a point 12 in FIG. 26). The refrigerant having the decreased temperature (at the point 12 in FIG. 26) is further compressed and heated to have a high temperature and a high pressure, and is discharged (at the point 1 in FIG. 26).

When the injection operation is not performed, an aperture of the expansion mechanism 61 is fully closed. That is, when the injection operation is performed, the aperture of the expansion mechanism 61 is larger than a predetermined aperture. However, when the injection operation is not performed, the aperture of the expansion mechanism 61 is set to be smaller than the predetermined aperture. Accordingly, the refrigerant does not flow into the injection pipe of the compressor 51.

The aperture of the expansion mechanism 61 here is controlled by electronic control by a control unit such as a microcomputer.

The operation of the heat pump device 100 at the time of a cooling operation is explained next. At the time of the cooling operation, the four-way valve 59 is set in a direction of a broken line. The cooling operation includes not only cooling used for air conditioning, but also drawing heat from water to make cold water, refrigeration, and the like.

The gas-phase refrigerant, which has become a refrigerant having a high temperature and a high pressure in the compressor 51 (at the point 1 in FIG. 26), is discharged from the compressor 51, and is heat exchanged by the heat exchanger 57, which functions as the condenser and the radiator, to be liquefied (at the point 2 in FIG. 26). The liquid-phase refrigerant liquefied by the heat exchanger 57 is pressure-reduced by the expansion mechanism 56, and becomes a gas-liquid two-phase state (at the point 3 in FIG. 26). The refrigerant, which has become the gas-liquid two-phase state in the expansion mechanism 56, is heat exchanged by the internal heat exchanger 55, and is cooled and liquefied (at the point 4 in FIG. 26). In the internal heat exchanger 55, the refrigerant, which has become the gas-liquid two-phase state in the expansion mechanism 56, is heat exchanged with the refrigerant (the point 9 in FIG. 26), which has become the gas-liquid two-phase state by pressure-reducing the liquid-phase refrigerant liquefied by the internal heat exchanger 55, by the expansion mechanism 56. The liquid-phase refrigerant (the point 4 in FIG. 26) heat exchanged by the internal heat exchanger 55 is branched to the main refrigerant circuit 58 and the injection circuit 62 to flow therein.

The liquid-phase refrigerant flowing in the main refrigerant circuit 58 is then heat exchanged with the refrigerant sucked into the compressor 51 by the receiver 54, and is further cooled (at the point 5 in FIG. 26). The liquid-phase refrigerant cooled by the receiver 54 is pressure-reduced by the expansion mechanism 53 and becomes the gas-liquid two-phase state (at the point 6 in FIG. 26). The refrigerant, which has become the gas-liquid two-phase state in the expansion mechanism 53, is heat exchanged by the heat exchanger 52, which functions as the evaporator, and is heated (at the point 7 in FIG. 26). At this time, because the refrigerant absorbs heat, water circulating in the water circuit 63 is cooled and used for cooling and refrigeration.

The refrigerant heated by the heat exchanger 52 is further heated by the receiver 54 (at the point 8 in FIG. 26), and is sucked into the compressor 51.

On the other hand, the refrigerant flowing in the injection circuit 62 is pressure-reduced by the expansion mechanism 61 (at the point 9 in FIG. 26) as described above, and heat exchanged by the internal heat exchanger 55 (at the point 10 in FIG. 26). A refrigerant (injection refrigerant) in the gas-liquid two-phase state, which has been heat exchanged by the internal heat exchanger 55, flows into the compressor 51 from the injection pipe of the compressor 51 keeping in the gas-liquid two-phase state.

The compression operation in the compressor 51 is the same as that of the heating operation.

When the injection operation is not performed, as in the heating operation, the aperture of the expansion mechanism 61 is fully closed, so as not to result in the refrigerant flowing into the injection pipe of the compressor 51.

In the above explanations, the heat exchanger 52 has been explained as a heat exchanger like a plate type heat exchanger that performs heat exchange between the refrigerant and water circulating in the water circuit 63. However, the heat exchanger 52 is not limited thereto, and may be other types of heat exchangers that perform heat exchange between a refrigerant and air.

The water circuit 63 may not be a circuit in which water is circulated, but may be a circuit in which another type of fluid is circulated.

As described above, the heat pump device 100 can be used for a heat pump device using an inverter compressor, such as an air conditioner, a heat pump water heater, a refrigerator, a freezer, and the like. 

1. A heat pump device comprising: a compressor having a compression mechanism for compressing a refrigerant; a motor that actuates the compression mechanism provided in the compressor; an inverter that applies a predetermined voltage to the motor; and an inverter control unit that causes the inverter to generate a high-frequency AC voltage having a de-energized section in which the voltage applied from the inverter to the motor is zero between a section in which the voltage is positive and a section in which the voltage is negative, wherein the inverter control unit includes: a current-value detection unit that detects a value of a current flowing to the inverter; and a high-frequency-voltage generation unit that causes the inverter to generate a high-frequency AC voltage according to a current value detected by the current-value detection unit.
 2. The heat pump device according to claim 1, wherein the current-value detection unit detects a current flowing from the inverter to the motor in the detection section.
 3. The heat pump device according to claim 1, wherein the current-value detection unit detects a DC current flowing to the inverter at at least any one of timing immediately before the start of the de-energized section and timing immediately after the end of the de-energized section of the detection section.
 4. The heat pump device according to claim 1, wherein the inverter has a serial connection part in which two switching elements are serially connected, and the current-value detection unit detects a current flowing to the serial connection part of the inverter, at at least any one of timing immediately after the end of the de-energized section and timing from immediately before the start of the de-energized section until the end of the de-energized section, of the detection section.
 5. The heat pump device according to claim 4, wherein the current-value detection unit detects a current flowing to a portion on a negative voltage side of the switching element on the negative voltage side, of the two switching elements in the serial connection part.
 6. The heat pump device according to claim 1, wherein the inverter is a three-phase inverter configured to parallely connect three serial connection parts each having two switching elements, and the de-energized section is a section in which of switching elements on a positive voltage side and switching elements on the negative voltage side of the three-phase inverter, all the switching elements on one side are on and all the switching elements on the other side are off
 7. The heat pump device according to claim 1, wherein the high-frequency-voltage generation unit causes the inverter to generate a high-frequency AC voltage with an amplitude being adjusted so that the current value becomes a predetermined value.
 8. The heat pump device according to claim 1, wherein the high-frequency-voltage generation unit causes the inverter to generate a high-frequency AC voltage adjusted to have an energization phase of the high-frequency AC voltage to the motor in which the current value is the largest of a plurality of energization phases that are set beforehand.
 9. The heat pump device according to claim 1, wherein the current-value detection unit detects a positive current value when the current value is positive and a negative current value when the current value is negative, at a predetermined timing, and the high-frequency-voltage generation unit causes the inverter to generate a high-frequency AC voltage adjusted so that a mean value of the positive current value and the negative current value approaches zero.
 10. The heat pump device according to claim 1, wherein the inverter control unit further includes a determination unit that estimates a winding temperature of the motor based on the current value, and when the estimated winding temperature is higher than a predetermined temperature threshold, stops the high-frequency-voltage generation unit from causing the inverter to generate a high-frequency AC voltage.
 11. The heat pump device according to claim 1, wherein the inverter includes is constructed of a switching element that is formed from a wide gap bandgap semiconductor or a MOSFET having a super junction structure. 12-13. (canceled)
 14. A heat pump system comprising a heat pump device including a refrigerant circuit in which a compressor having a compression mechanism that compresses a refrigerant, a first heat exchanger, an expansion mechanism, and a second heat exchanger are sequentially connected by piping; and a fluid utilization device that utilizes fluid heat-exchanged with the refrigerant by the first heat exchanger connected to the refrigerant circuit, wherein the heat pump device further includes: a motor that actuates the compression mechanism provided in the compressor; an inverter that applies a predetermined voltage to the motor; and an inverter control unit that causes the inverter to generate a high-frequency AC voltage having a de-energized section in which a voltage applied from the inverter to the motor is zero between a positive section in which the voltage is positive and a negative section in which the voltage is negative, and wherein the inverter control unit includes: a current-value detection unit that detects a value of a current flowing to the inverter; and a high-frequency-voltage generation unit that causes the inverter to generate a high-frequency AC voltage according to a current value detected by the current-value detection unit.
 15. A method for controlling an inverter in a heat pump device including: a compressor having a compression mechanism that compresses a refrigerant; a motor that actuates the compression mechanism provided in the compressor; and an inverter that applies a predetermined voltage to the motor, the method comprising: a high-frequency-voltage generating step of causing the inverter to generate a high-frequency AC voltage having a de-energized section in which a voltage applied from the inverter to the motor is zero, between a positive section in which the voltage is positive and a negative section in which the voltage is negative; and a current-value detecting step of detecting a value of a current flowing to the inverter, wherein at the high-frequency-voltage generating step, the inverter is caused to generate a high-frequency AC voltage according to a current value detected by the current-value detecting step.
 16. The heat pump device according to claim 1, wherein the inverter is configured based on a serial connection circuit having two switching elements provided on a positive voltage side and a negative voltage side, respectively.
 17. The heat pump device according to claim 1, wherein the current-value detection unit detects a value of a current flowing to the inverter in a detection section from immediately before a start of the de-energized section to immediately after an end of the de-energized section. 